<template>
    <div class="slider" ref="slider">
        <div class="slider-group" ref="sliderGroup">
            <slot>
            </slot>
        </div>
        <div class="dots">
            <span class="dot" :class="{active: currentPageIndex === index }" v-for="(item, index) in dots"></span>
        </div>
    </div>
</template>

<script type="text/ecmascript-6">
  import {addClass} from 'common/js/dom'
  import BScroll from 'better-scroll'

  export default { //轮播图组件
    name: 'slider',
    props: {
      loop: {
        type: Boolean,
        default: true
      },
      autoPlay: {
        type: Boolean,
        default: true
      },
      interval: {
        type: Number,
        default: 4000
      }
    },
    data() {
      return {
        dots: [],
        currentPageIndex: 0
      }
    },
    mounted() {
      setTimeout(() => {
        this._setSliderWidth()
        this._initDots()  //必须保证在_initSlider前面初始化，否则this.children.length会多出两个
        this._initSlider()

        if (this.autoPlay) {
          this._play()
        }
      }, 20)

      window.addEventListener('resize', () => {
        if (!this.slider) {
          return
        }
        this._setSliderWidth(true)
        this.slider.refresh()
      })
    },
    destroyed() {
      clearTimeout(this.timer)
    },
    methods: {
      _setSliderWidth(isResize) {
        this.children = this.$refs.sliderGroup.children

        let width = 0
        let sliderWidth = this.$refs.slider.clientWidth
        for (let i = 0; i < this.children.length; i++) {
          let child = this.children[i]
          addClass(child, 'slider-item')

          child.style.width = sliderWidth + 'px'  //不要忘记加单位！
          width += sliderWidth
        }
        if (this.loop && !isResize) {  //如果loop为true,BScroll的snap属性会左右克隆两个DOM，保证循环切换
          width += 2 * sliderWidth
        }
        this.$refs.sliderGroup.style.width = width + 'px'  //不要忘记加单位!
      },
      _initSlider() {
        this.slider = new BScroll(this.$refs.slider, {
          scrollX: true, //横向滚动
          scrollY: false, //禁止纵向滚动
          momentum: false, //禁止惯性运动
          snap: true,
          snapLoop: this.loop,   //better-scroll1.0以后没有了，使用0.1.15版本的
          snapThreshold: 0.3,
          snapSpeed: 400
        })

        this.slider.on('scrollEnd', () => {  //每次切换到下一张之后，会派发一个scrollEnd事件
          let pageIndex = this.slider.getCurrentPage().pageX
          if (this.loop) {
            pageIndex -= 1
          }
          this.currentPageIndex = pageIndex

          if (this.autoPlay) {
            clearTimeout(this.timer)
            this._play()
          }
        })
      },
      _initDots() {
        this.dots = new Array(this.children.length)
      },
      _play() {
        let pageIndex = this.currentPageIndex + 1  //从0开始的,需要+1
        if (this.loop) {
          pageIndex += 1  //loop为true时，最开始有一个复制的副本，实际的pageIndex需要+1
        }
        this.timer = setTimeout(() => {  //页面的切换，利用BScroll的接口goToPage
          this.slider.goToPage(pageIndex, 0, 400)  //参数：X方向、Y方向、时间间隔
        }, this.interval)
      }
    }
  }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
    @import "~common/stylus/variable"

    .slider
        min-height: 1px
        .slider-group
            position: relative
            overflow: hidden
            white-space: nowrap
            .slider-item
                float: left
                box-sizing: border-box
                overflow: hidden
                text-align: center
                a
                    display: block
                    width: 100%
                    overflow: hidden
                    text-decoration: none
                img
                    display: block
                    width: 100%
        .dots
            position: absolute
            right: 0
            left: 0
            bottom: 12px
            text-align: center
            font-size: 0
            .dot
                display: inline-block
                margin: 0 4px
                width: 8px
                height: 8px
                border-radius: 50%
                background: $color-text-l
                &.active
                    width: 20px
                    border-radius: 5px
                    background: $color-text-ll
</style>
